To measure the relative position of two machine parts, a measuring graduation is disposed on one of the machines parts, and a scanning unit is disposed on the other one of the relatively movable machine parts. During position measurement, the measuring graduation is scanned by the scanning unit, and position-dependent mutually phase-shifted analog scanning signals are generated.
Both the physical scanning principle and the grating period of the material measure need to be selected according to the intended use of the position-measuring device. In the case of magnetic and inductive scanning principles, only relatively large grating periods are feasible because of physical constraints. These scanning principles have the advantage of allowing for relatively large mounting tolerances. However, when scanning with a scanning unit, a large grating period produces analog scanning signals having a signal period that corresponds to this relatively large grating period. It has been found that these analog scanning signals have such a high quality that analog signals having a varied, in particular reduced, signal period can be generated therefrom using relatively simple means.
In the case of optical scanning principles, much smaller graduation periods are attainable than in the case of other scanning principles, making it possible to obtain analog scanning signals having a small signal period. However, this signal period may be too small for subsequent electronics, so that, here too, the signal period needs to be varied, in this case increased.
The analog output signals which are synthetically generated by the position-measuring device and whose signal period is reduced or increased compared to the scanning signals can be fed to subsequent conventional electronics for further processing.
Approaches for synthetically generating analog output signals having a varied signal period are found in EP 1 399 715 B1 and EP 1 606 590 B1. Our invention is based on EP 1 399 715 B1.
According to EP 1 399 715 B1, the variation, here reduction, of the signal period of two mutually phase-shifted sinusoidal analog scanning signals is accomplished by means of a module which receives the analog scanning signals as input signals and is adapted to generate therefrom two digital position signals which are representative of the position and whose frequency is a multiple of that of the input signals. These position signals are sequences of data words, each of which represents a value of the SIN signal or COS signal, respectively.
Connected downstream of this module is a digital-to-analog converter adapted to generate, from these digital sinusoidal position signals, mutually phase-shifted analog sinusoidal output signals whose frequency is a multiple of that of the scanning signals, and to make these analog sinusoidal output signals available at the output.